An inertial measurement unit (IMU) can be placed on a body to capture motion of the body. Multiple IMUs can be placed at different points on a hinged body in an effort to detect motion at different parts of the body. One example of a hinged body is the body of a person. However, IMUs can have difficulty in keeping track of absolute orientation over a long period of time due to limits on their the ability to accurately detect some types of motion. The present orientation being used by an IMU may drift over time so that the present orientation being used no longer accurately corresponds to the true or absolute orientation of the IMU. Furthermore, the drift which occurs in one IMU will differ from that which occurs in another IMU. Variations in drift will prevent an accurate assessment of motion of one part of the body relative to another part of the body. For example, variations in drift may cause IMUs on two different parts of a person's body to indicate that the two parts of the body are moving in different directions when they are actually moving in the same direction.
Accordingly, when multiple IMUs are being used on the same body, there is a need to make corrections to the present orientation being used by each IMU to allow for an accurate determination of relative motion among the different parts of the body on which the IMUs are placed. There is a further need to make the corrections without the use of additional sensors and without a modification of the environment in which the IMUs operate.